1. Field of the Invention
The present invention relates generally to a fuel vapor treatment system configured to be used with an internal combustion engine for an automobile. More specifically, the present invention relates a fuel vapor treatment system equipped with a leak diagnosing system.
2. Background Information
A conventional fuel vapor treatment system for an internal combustion engine is configured to direct fuel vapor produced in a fuel tank into a canister so as to allow the fuel vapor to be temporarily adsorbed. The fuel vapor adsorbed in the canister is then sent to an air intake system of the internal combustion engine by introducing fresh air into the canister through a fresh air introducing port and allowing the fresh air and fuel vapor to be drawn into the air intake system through a purge control valve. In this way, fuel vapors are prevented from being released to the outside air.
However, if a crack develops in the piping of the purge line running from the fuel tank to the canister and from the canister to the purge control valve, or if a poor seal occurs at a joint portion of the piping, then fuel vapor will leak out and the fuel vapor treatment system will not be able to sufficiently prevent the release of fuel vapor to the outside air.
In response to the possibility of such a leak, leak diagnosing systems have been contrived that are configured to determine if fuel vapor is leaking from the purge line. One such leak diagnosing system is disclosed in Japanese Laid-Open Patent Publication No. 2003-56416. In the system disclosed this publication, the purge line is closed off after the engine is stopped by closing the purge control valve and closing a fresh air introducing port on/off valve that is arranged and configured to open and close the fresh air introducing port (which is open to the atmosphere). After the purge line is closed off, the purge line pressure rises in accordance with a temperature rise and the leak diagnosing system detects the purge line pressure repeatedly at a prescribed frequency (once per prescribed amount of time). The leak diagnosing system determines that the purge line is normal if a summation value of the detected purge line pressures is equal to or larger than a threshold value and that the purge line is leaking if the summation value is smaller than the threshold value.
Another leak diagnosing system is disclosed in Japanese Laid-Open Patent Publication No. 2001-12316. This leak diagnosing system is configured to introduce a prescribed negative pressure to the purge line when a diagnosis condition is satisfied while the engine is running and then close off the purge line. The leak diagnosis system determines if a leak exists based on the rate of change of the purge line pressure after the purge line is closed off.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved leak diagnosing system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.